Spark plug elbow and barrel sealing grommet



Jan. 13, 1953 J. D. FRAZEE 2,625,579

SPARK PLUG ELBOW AND BARREL SEALING GROMMET Filed Feb. 9, 1950 lac-veHwtor John D.Fraze 9W nmzfi Patented Jan. 13, 1953 SPARK PLUG ELBOW AND BARREL SEALING GROMMET John D. Frazec, Glastonbury, Cnn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application February 9, 1950, Serial No. 143,265

6 Claims. (01. 174-77) This invention relates to an improvement in electrical connections and refers particularly to an improved connection between a spark plug and an ignition cable of an internal combustion engine.

An object of this invention resides in the provision of a connection between the spark plug and ignition cable which is detachable and rewireable. This permits easy replacement of parts sincedetail parts may be removed and replaced. This replacement of detail parts reduces the expense necessary to keep an ignition system in the best of condition since whole assemblies need not be discarded when only a small part thereof actually needs replacing.

A further object resides in the provision of an improved union between the ignition cable and spark plug which includes a resilient grommet which provides an effective seal against moisture entering the spark plug cylinder from the ignition harness. This grommet also seals the spark plug from electrical flashover. The use of a corona shield in said grommet tends to reduce the formation of corona.

In the drawing,

Fig. 1 is an elevation view partly in section of an internal combustion engine spark plug, and part of an ignition shield connected by an elbow construction embodying the present invention.

Fig. 2 is a view partly in section showing a modification of the grommet.

Referring to the drawings in detail, the spark plug generally indicated at 2 is of the conventional type in common use on aircraft engines and consists of one part.

The spark plug 2 has at its lower end an external threaded portion 6 adapted to be screwed into an internally threaded aperture in an engine cylinder, and a polygonal wrench receiving portion 8. Ground electrodes H) are made integral with said spark plug so that when the spark plug is in its engine operating position they extend down into the engine cylinder.

The upper end of the spark plug 2 is formed as a metallic cylinder l4 externally threaded at l6. Fixed within the spark plug is the spark plug core including a metal electrode I8 and insulating material. This metal electrode 18 fits into the lower end of the spark plug to form gaps with ground electrodes It]. The insulating material referred to above is used to prevent electrical contact between the metal electrode l8 and any part of the spark plug 2, it consists of material immediately surrounding the metal electrode I8 as at 20 and a coating around the inner side of the cylinder [4 shown at 22. The

end of the electrode l8 within the cylinder I4 is peened over the contact button 19 as at 2|.

The spark plug elbow 24 used to protect the insulated cable 26 as it bends near the spark plug, consists of an elbow 28 having a ferrule attached on each end such as by silver soldering or brazing. This ferrule may be formed integral with said elbow if desired. The ferrule 31! on one end is externally threaded at 32 and has a countersunk portion 34 the purpose of which is to be disclosed hereinafter. The ferrule 36 on the opposite end has a flange 38 for engaging a cooperating flange 40 on a union nut 42, internally threaded at 44, which is placed over the elbow before the ferrules are attached. This union nut 42 cooperates with the externally threaded upper end l6 of the cylinder 14 to provide a rigid connection between the spark plug elbow 24 and the spark plug 2.

The ignition shield 48 of the harness consists of a flexible metallic tube 50 having a ferrule 52 attached to one end such as by silver soldering or brazing. Said ferrule having a flange 54 for engaging a cooperating flange 56 on a union nut 58, internally threaded at 60, which is placed over the tube before the ferrule is attached. This union nut 58 cooperates with the externally threaded part 32 of ferrule 30 to provide a rigid connection between the ignition shield 48 and the spark plug elbow 24. The other endof the shield may be attached to a harness by any means desired.

The insulated cable 26 referred to above is a lead-in from an electrical source (not shown). and consists of a conductor 62 coated with a resilient insulated covering 64. One end (not shown) is attached within a harness, by any means desired, to the electrical source referred to above. The other end of the conductor at 66 is inserted in a hole 66 in a metal stud 10. The stud is held on the wire by being crimped at 12. The metal stud ID has a flanged portion 74 of the same diameter as the insulated covering 64 of the conductor 62. This flange 14 fits against the covering 64. The remainder of the stud is externally threaded at 16 to provide a means for attaching said cable to form an electrical contact and hold it in place in a manner to be described hereinafter.

A grommet 18 within the spark plug elbow 24 and upper part of the cylinder [4 of the spark plug 2 is a member formed as a tube of resilient material. The outside portion within thespark plug elbow 24 fits tightly from a recess 80 in ferrule 36 to the countersunk portion 34. This portion may be sealed with a cement to further insure against moisture leakage from the harness. This part of the grommet within said elbow also provides extra insulation against heat. A flange 82 on the grommet fits in the recess 86 and is held therein in its assembled position between that end of the elbow and the top of cylinder I4 of the spark plug. This flange 82 seals the spark plug 2 from moisture leakage and serves to prevent the grommet 1-8 from being blown out in the event of gas leakage through said spark plug. The flange also governs the amount of the grommet which extends into elbow 24 and into cylinder l4. 4 H

The outside portion of the grommet within the cylinder l4 has a diameter smaller than-the diameter of the cylinder and is provided with sealing rings 84 which form a seal with the cylinder 14. The relief in the areas between the sealing rings 84 prevents the grommet 18 from sticking to thei'ns'ideofthe spark plug-cylinder 14. The sealing rings 8'4seal the sparkplugcylinderfrom electrical fiashove'r to the top of the cylinder.

The inside portion "or the grommet within the elbow 'fit's tightly around the cable 26 passing through the elbow. This tight 'fit seals against the passage of moisture into the spark plug and the escaping of gas vapor th'rough'the spark plug cylinder. The'insid'e'portion within the cylinder contains a circular flange 8'6. The cable 26 also fits tightly within thisinside portion up to said flange. Thethread'ed'portion I6 ofthe "stud 10 on the end of the cable extends through said flange for a purposet'o be described hereinafter.

A skirt 88 is fermed below the flange 86. A metallic'cup90 fitting within said skirt'a'ndhaving a hole 92 in the bottom thereof'for allowing the threaded portion 16 of stud 10 to extend through may be inserted intosaid skirt. 'This copper or bras 'cordna shieldlowe'rs'the Voltage stress to the surrounding air by increasing the effective area of the conductor and thereby reducing the formation 'of corona. A'spri'ng 94 and spring retainer 96 is "provided to make a "good electrical eontac't between the stud "l0 and electrode l8 ermesparkpiug. The spring 94 may be fixed on the internally threaded epriiig "recameras by anym'eans available as long as an electrical contac is "made therebetwe'en. The threadedportion 160i the'stud l0 screws into the spring retainer 96. This "provides an electrical contact between the stud I0 and spriiig'retamer 96. The flange fi'compressed therebetweenholds the cable 26 and'spring94 inpl'ac'e. Thespring in its extended position is longer than theski'rt 88,asshow'n in Fig. 2,"s'othat'a positiveeo'ntact ismade with'the electrode l8.

The length of the grommet 18 disassembled, from the flange 82 "to the bottom of'the skirt 88, is longer than the depthof'the cylinderl l from its top to the top of the insulating material '29 around the electrode l8, so that the lower edge of said skirtis forced against theinsulatingmaterial around said spring and contact button 19 forming aseal when the grommet is in its assembled position. I

A second grommet I00 within the shield 48 is also a member formed as a tube of resilient material. On one end is a flange I02 tapered to fit into the countersunk'portion 34 of the ferrule 39 of the spark plug "elbow 24. The other end fits tightly'into'the shield"48 'with'the cable "26 also fitting tightly-as it passes therethrough. The flange l-02isheld between the face ofthecounte'r- 4 sunk portion 34 of the elbow 24 and the cooperating end of the ferrule 52 of the cable 48. This grommet I66 aids in preventing grommet 18 from being forced out of the elbow 24 by leakage of gas through the spark plug 2.

Fig. 2 is a modification of the grommet 18 as shown in Fig. 1. This grommet lil l difiers from grommet I8 mainly in the connecting and holding means used to make an electrical connection between the conductor 52 of cable 26 and spring :94, and to hold the cable 26 and spring 94 in place.

7 This modification has in place of the single fiange 86 in grommet I8, a flange I08 with a molded-ininsert I08 below it. Said insert has an internally threaded bore H0 adapted to receive the threaded end 760i stud i6, and an externally threaded boss 2 which extends into skirt 88 adapted to screw into aspring retainer 96.

The connection as shown in Fig. 1 can be assembled by one of two methods, depending on whether or not 'the connection is being made while the harness is apart or while the harness is on the engine. The method of assembling the connection, considering the harness to be on the engine, is as follows:

The ignition shield 48 is slipped over the cable 26, which is attached within the harness and extends out therefrom, and attached to the harness by any means desired. Then the grommet I66 is slipped over the conductor 26 and into'the ignition shield 48, The cable 26, with its metal stud '10 on the end, is inserted through the spark plug elbow 24, and pulled through as far as it will go. The cable is made 'so that a few'inches are provided within the harness to permit the cable to be extended that distance over the minimum length necessary in its assembled position. Then the cable 26 is inserted in the grommet 18 until the externally threaded portion 16 of stud 10 extends through the flange 86 into skirt 88. The spring retainer 96 is screwed on stud T0 with spring 94 attached. The grommet "I8 is then pulled back into the sparkplug elbow 24 until flange 82 on the grommet fits in recess 86 in ferrule 36. Then the spark plug elbow 24 and ignition shield 48 are connected rigidly together by the means provided and disclosed hereinbefore. The end of the grommet 18 projecting from the elbow 24 is then inserted in the cylinder [4 of a spark plug 2. The spark plug elbow 2'4 and spark plugz are then rigidly connected 'together'by the means provided and disclosed hereinbefore. If a cement istobe used, fo'rexample as referred to above, it can be put on at anytime before the parts to be placed together are finally positioned.

The only difference between the method "disclosed above and'the method using'the grommet I04 ofFig. 2, is that the spring retainer 96 need not be installed before the grommet is drawn into the spark plug elbow 24 since the cable 26 is held in the grommet by the molded-in insert I98. The spring retainer'SS and spring 94"can be put in place anytime before the grommet is inserted into the spark plug cylinder I 4.

The method of assembling the connection, considering the harness to be apart, is as follows:

The cable 26, with its metal stud 1|) on the end, is insertedinto the grommet '18 until theexternally threaded portion'Hi of the stud extends-through the flange 86 into skirt 88. The spring retainer 96 is screwed on stud-10 with spring 94 attached. The free end-ofcable26 is theninsertedintosparkplug 'elbow 2 4 and pulled from the opposite end until flange 82 on the grommet fits in recess 80 in ferrule 36. Then the grommet I00 is slipped over the free end of the cable 26 and pushed down until the tapered flange I02 fits against the countersunk portion 34 of ferrule 30. The free end of the cable 26 is then inserted into the ignition shield 48 and drawn through until the end of ferrule 52 fits against the flat side of the tapered flange I02. The spark plug elbow 24 and ignition shield 43 are then connected rigidly together by the means provided and disclosed hereinbefore. The remaining two steps of this method are identical to the last two steps of the other methods described above.

Here again, the only difference between the method disclosed immediately above and the method using the grommet I04 of Fig. 2, is that the spring retainer 96 need not be installed before the grommet I04 is drawn into the spark plug elbow 24 since the cable 26 is held in the grommet I04 by the molded-in insert I08. The spring retainer 96 and spring 94 can be put in place any time before the grommet is inserted into the spark plug cylinder l4.

While a suitable mechanical embodiment in two slightly different forms has been hereinabove described and illustrated in the accompanying drawing for the purpose of disclosing the invention, it is to be understood that the invention is not limited to the particular embodiment so illustrated and described, but that such changes in the size, shape and arrangement of the various elements and of the materials of Which they are formed may be resorted to as come within the scope of the sub-joined claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. A grommet for use in a connection between a spark plug having a cylinder provided with an internal seating surface and an adjacent connector, said grommet consisting of a sleeve of resilient material for projection in part into said connector and in part into said cylinder, said sleeve having an external flange, said flange being adapted to be held between said connector and said cylinder, the portion of the sleeve adapted for projection within said connector being adapted dimensionally to have a slidable fit in the connector, the portion of the sleeve adapted for projection into said cylinder having a sealing ring adapted dimensionally to have a slidable fit in the cylinder, a part of the sleeve below said ring forming a skirt, the length of said portion adapted for projection into said cylinder being adapted dimensionally so that it is longer than the inner depth of the cylinder to the seating surface so that when said last named portion is in its assembled position the lower edge of said skirt is adapted to be forced against the seating surface of said cylinder forming a seal.

2. In combination, a cylinder provided with an internal seating surface, an electrical contact member located on said seating surface, a grommet including a sleeve of resilient material projecting in part into said cylinder, said sleeve having a flange determining the portion thereof extending into said cylinder, means for holding said flange against the open end of said cylinder, the part of the sleeve projecting into said cylinder having a sealing ring thereon, said sealing ring having a slidable fit against said cylinder, the end of said sleeve projecting into said cylin- 6 der being deformablypositioned against the seat ing surface of said cylinder and forming a seal around said contact member.

3. In combination, a cylinder provided with an internal seating surface, an electrical contact member located on said seating surface, a connector connected to the open end of said cylinder, a grommet consisting of a sleeve of resilient material projecting in part into said connector and in part into said cylinder, said sleeve having a flange determining the portions thereof extending respectively into said connector and cylinder, said flange being held between said connector and said cylinder, the part of the sleeve projecting into said connector having a slidable fit therein, the part of the sleeve projecting into said cylinder having a sealing ring thereon, said sealing ring having a slidable fit in said cylinder, the end of said sleeve projecting into said cylinder being forced against the seating surface of said cylinder forming a seal around said contact member.

4. A grommet for use in a spark plug having a cylinder provided with an internal seating surface, including a sleeve of resilient material for projection into said cylinder, said sleeve having sealing rings, said sealing rings adapted dimensionally to have a slidable fit against the sides of the cylinder, and the end of said sleeve adapted to project into said cylinder being adapted to be deformably positioned against said seating surface to provide a seal with said seating surface.

5. In combination, a cylinder provided with an internal seating surface, an electrical contact member located on said seating surface, a connector connected to the open end of said cylinder, a grommet consisting of a sleeve of resilient material projecting in part into said connector and in part into said cylinder, said sleeve having a flange determining the portions thereof extending respectively into said connector and cylinder, said flange being held between said connector and said cylinder, the part of the sleeve projecting into said connector having a slidable fit therein, the part of the sleeve projecting into said cylinder having a sealing ring thereon, said sealing ring having a slidable fit in said cylinder, the end of said sleeve projecting into said cylinder being forced against the seating surface of said cylinder forming a seal around said contact member, an insulated conductor extending into said grommet, and means for making contact between the end of said conductor in said grommet and said contact member.

6. In combination, a spark plug having a cylinder provided with an internal seating surface, an electrical contact member located on said seating surface, a tube, a connector connecting said cylinder to said tube, a first grommet consisting of a sleeve of resilient material projecting in part into said connector and in part into said cylinder, said sleeve of said first grommet having a flange determining the portions thereof extending respectively into said connector and cylinder, said flange being held between said connector and said cylinder, the part of the sleeve projecting into said connector having a slidable flt therein, the part of the sleeve projecting into said cylinder having a sealing ring thereon, said sealing ring having a slidable fit in said cylinder, the end of said sleeve projecting into said cylinder being forced against the seating surface of said cylinder forming a seal around said contact memher, a second grommet consisting of a sleeve of resilient material projecting in part into said tube and in part into .said connector, said sleeve of said second grommet having aflange determin- REFERENCES CITED The following references are of 'record'in the file of this patent:

UNITED STATESPATENTS Number Name Date 382,767 Patterson May 15, 1888 2,177,268 Stone et a1 Oct. 24, .1939 2,278,448 Ingalls Apr. 7, .1942 2,280,855 .Rose Apr. 28, 1942 2,381,595 Hulfish Aug. '1, 1945 2,399,390 Robertson Apr. 30, 1946 2,463,924 Van Orden Mar. 8,, 1949 

